A member of the public stepped in to help a police officer who was injured in an incident near Makarora, between Wanaka and Haast.
The constable was taking a man to Wanaka police station when he was attacked, police said.
The officer had stopped a driver at Makarora about 2pm for a routine breath test, which he failed.
On the drive back to Wanaka, the man allegedly assaulted the officer, senior sergeant Allan Grindell said.
He managed to stop the patrol car near a roadside cafe where he called out for help, and a member of the public stepped in until other police officers, a fire service crew and St John Ambulance arrived.
The officer suffered minor inuries to his head, eye and ribs and was treated at the local medical centre.
The driver was taken to Wanaka police station and was likely to face charges relating to drink driving and assault on a police officer.
- The Southland Times